U.S. and European aviation regulators concurrently imposed emergency inspection requirements for the type of jet engine that broke apart in Tuesday’s fatal Southwest Airlines Co. accident, calling for more engines to be scrutinized, on a faster timetable, than previously contemplated.

Accident investigators believe the engine in Tuesday’s accident broke apart because a fatigue crack on the interior part of a fan blade caused the component to separate, triggering an uncontained engine failure that spewed parts into the exterior...